1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a motion compensation, and more particularly, to performing a motion compensation to prevent a motion-induced distortion from occurring during 3:2 pull down and 2:2 pull down.
2. Description of the Related Art
As large-sized display devices such as plasma display panels (PDP) and liquid crystal display (LCD) devices are coming into increasing use in recent years, many users are able to enjoy movies at home through the large-sized display devices as if they are in movie theaters.
Film projected at movie theaters runs at 24 or 25 frames per second. The created frames are stored in films and are displayed on a screen in a progressive scan method. The progressive scan method refers to a method that displays a single scene on a screen in a single time in the unit of frame.
Most display devices currently used adopt an interlaced scan method which is in contrast to the progressive scan method. The interlaced scan method divides a single scene into at least two fields and displays the divided fields on a screen in sequence. Such display devices process and display images in different ways according to their respective transmission standards. For example, according to the national television system committee (NTSC), the display device processes an image with 60 fields per second, and according to the phase alternation line (PAL) or sequential couleur a memoire (SECAM), the display device processes an image with 50 fields per second.
If the film is reproduced on an interlaced display device, a user suffers from a rapid moving of images due to the difference in the number of frames displayed per second. Accordingly, in order to reproduce the film through the interlaced display device, the display device has to increase the number of fields using an image conversion apparatus such as telecine (which is a compound word of “television” and “cinema”).
More specifically, in order to display a film on an NTSC display device, 24 frames per second have to be increased to 60 fields, and in order to display a film on a PAL or SECAM display device, 25 frames per second have to be increased to 50 fields. These operations are referred to as 3:2 pull down and 2:2 pull down. Meanwhile, in order to display a pull down image format on a progressive display device, an inverse telecine process is required.
FIGS. 1A and 1B are views illustrating a conventional image format conversion method.
In FIGS. 1A and 1B, T1 denotes a top field of a frame 1 and B1 denotes a bottom field of the frame 1, T2 denotes a top field of frame 2 and B2 denotes a bottom field of the frame 2, T3 denotes a top field of a frame 3 and B3 denotes a bottom field of the frame 3, and T4 denotes a top field of a frame 4 and B4 denotes a bottom field of the frame 4.
Referring to FIG. 1A, 5 fields are obtained from 2 frames such that 60 fields are obtained from 24 frames per second. More specifically, 3 fields are obtained from each of the frame 1 and the frame 3, and 2 fields are obtained from each of the frame 2 and frame 4. Herein, either the top field or the bottom field is repeated such that 3 fields can be obtained from one frame of a film.
The video fields obtained by performing the 3:2 pull down are converted into progressive frames using an inverse telecine process. More specifically, the top field T1 and the bottom field B1 are combined to create 3 frames, the top field T2 and the bottom field B2 are combined to create 2 frames, the top field T3 and the bottom field B3 are combined to create 3 fields, and the top field T4 and the bottom field B4 are combined to create 2 fields.
Referring to FIG. 1B, 2 fields are obtained from 1 frame such that 50 fields are obtained from 25 frames per second. That is, a top field and a bottom field are obtained from each frame. The video fields obtained by performing the 2:2 pull down are converted to progressive frames using an inverse telecine process. That is, the top field and the bottom field are combined to create two frames.
According to the image format conversion method as described above, two or three frames have the same motion phase. For example, the frames T1+B1, B2+T2, B3+T3, and T4+B4 have the same motion phase.
When the progressive frames generated using the inverse telecine process are displayed on a screen, two or three frames are repeatedly displayed on the screen, which causes a motion judder. In order to prevent the motion judder, a motion compensation is performed. The motion compensation estimates a motion based on adjacent images and creates an intermediate image. The motion compensation is disclosed in the U.S. Pat. No. 5,929,919, titled “Motion-compensated Field Rate Conversion”.
However, in U.S. Pat. No. 5,929,919, since the motion compensation is performed with respect to all of the incoming fields during the 3:2 pull down, a motion estimation error-induced distortion, such as halo, block effect, and false matching, is likely to occur. Also, a fall-back detection circuit to perform a motion refinement for the more accurate motion detection is additionally required.